Surface treating appliances in general, and particularly cylinder-type vacuum cleaners, typically are provided with a cleaner head that can be moved back and forth over a cleaning surface. Sometimes such a cleaner head will have an agitator or ‘brush bar’ driven by a drive assembly. On a textile covered floor surface, for example, the brush bar works to agitate the floor surface so as to encourage dirt particles to be released from the nap of the carpet, therefore generally improving dirt pick up performance over a ‘passive’ cleaner head not having a brush bar.
In most cases, the drive assembly comprises an electric motor and a belt to transmit power from the motor to the brush bar. Typically, the transmission belt will engage with one end of the brush bar and so the electric motor will be mounted to one side of the cleaner head so that the transmission belt may have a straight run to the brush bar. Since the motor is mounted off-centre, this generates an out-of-balance torque that tends to rotate the cleaner head relative to its neck as the cleaner head is lifted from the floor during use—this effect becomes particularly pronounced with heavier motors. This ‘droop’ of the cleaner head can be an annoyance for a user when, during use, the user attempts to ‘lift and place’ the cleaner head on the floor, for example to traverse steps in the surface or to transition the cleaner head between successive stairs on a staircase. To compensate for this, a user may try and ‘lift and place’ the cleaner head more quickly which tends to impose greater impact loads on the cleaner head thereby increasing the likelihood of the cleaner head being damaged.